Fermentation extracts containing fibrolytic enzymes,which were previously used mainly for nonruminants, are now being used in
ruminant rations following feeding trials in which some benefit has been observed . The nutritional benefit from the supplementation appears to depend on many factors, most of which have yet to be evaluated. The effectiveness of enzymes varies with diet
and with the component of the diet to which the enzyme additive is added .
The prefeeding phase seems likely to be important, and increased postruminal digestion has been demonstrated . Some enzymes are sufficiently stable to pass from the rumen and be active in the abomasum and beyond, suggesting that the enzymes
may aid the digestion of feed materials that escape
ruminal fermentation. However, one of the most interesting
possibilities is that the enzymes stimulate fiber digestion in the rumen. Present information about this possibility is mixed. Carboxymethylcellulase (CMCase) and xylanase activities did not increase in response to enzyme addition to the feed, yet infusion of enzymes directly into the rumen increased enzyme activities in ruminal fluid. Furthermore, a recent in vitro study
indicated that there was some synergism between feed additive and ruminal enzymes.
The present study was undertaken to investigate the effects of adding enzymes directly to ruminal digesta in vitro; to determine whether enzyme supplements added without prior incubation with the feed, in order to eliminate prefeeding effects, could stimulate the rate
of digestion of corn and grass silages; and to identify the likely nature of the key enzyme activities.